1. Field of the Invention
This invention relates generally to ground current interrupter circuits, and more specifically, this invention relates to a ground fault current interrupter that is actuated to break the power line when undesired arcing occurs between the power line and a metal sheath or cover for the power cable, as well as in the presence of a ground fault current.
2. Description of the Prior Art
Ground fault current interrupter (GFCI) circuits are used to protect against an undesired grounding of a power line, such as by a person inadvertently being connected from the power line to ground at an outlet in the home. A common form of such a ground fault current interrupter circuit includes a differential transformer with opposed primary windings, one primary winding being associated with the power line and the other being associated with the neutral return line. If a ground fault should occur on the load side of the GFCI circuit, the two primary windings will not cancel, with the result that a flux flow is produced in the core of the differential transformer. This resultant flux flow is detected by a secondary winding on the differential transformer core, and this secondary winding then produces a trip signal for a circuit opening arrangement to open the power line.
While such GFCI circuits have protected many people from serious injury or death in the event of a ground fault current, there are other types of hazardous situations that are not protected against by the basic GFCI circuit. Thus, for example, in U.S. Pat. No. 4,598,331, arrangements are shown for protecting against potentially hazardous situations such as an open neutral or ground lead, an excessive voltage between the neutral lead and the ground lead, and reversal of input connections between the power and neutral lines. However, there are concerns with respect to electrical power cords and equipment other than these situations that are potentially hazardous to a person using the equipment.
One such concern relates to the arcing between a power line and a metallic sheath or cover that may occur in electrical power cords or cables. Such electrical arcing may not be a direct threat to an individual person, but it can result in combustion. The resulting fire is potentially hazardous to both health and property.
Accordingly, it would be desirable to have a GFCI circuit that is capable of protecting against undesired arcing, as well as against the ground fault currents that are the basic protective function of the GFCI circuits.